It is to utilize the valuable biological and physiological properties of native oils. In addition to the obvious utilization known for the longest time, i.e. the use of native oils for alimentary purposes, a number of such oils (e.g. almond oil, peanut oil and soybean oil) proved to be very useful as a basic material or therapeutic adjuvant used as a carrier of oily percutaneous or intramuscular injection solutions and as ointment bases in the pharmaceutical and cosmetical industries. The use of various vegetable oils such as wheat-germ oil, maize-germ oil, pumpkin seed oil and cotton seed oil, are also used in alimentation or the prevention of the arteriosclerosis, however, no widespread utilization of vegetable oils has been made for therapeutical purposes.
This can only partly be explained by the fact that no botanically well-defined plant species were available to the users which could provide a defined and reproducible composition of the oils obtained by known methods.
A more significant difficulty in employing these oils in therapeutics was due to the fact that 90 to 95% of the components, mainly lipids, representing the active ingredients of vegetable oils consist of unsaturated or polyunsaturated fatty acid glycerides with a tendency to oxidation (rancidity), raising severe problems of stability, and these problems were not solved heretofore.
Drugs were made available lately in capsule form. This can be explained by many advantageous properties of capsules, such as the rapid biological availability, sustained action, and stability.
The efficiency of the protection of an active ingredient filled into capsules against outside environmental influences (oxygen of the air, moisture, heat) depends on the material of the capsule wall. In addition to gelatine, the wall of the soft gelatine capsules (which are also popular for the relatively simple preparation) also contains liquid, nontoxic additives such as polyethylene glycol, sorbitol and glycerol according to the requirements of modern encapsulating machines (e.g. U.S. Pat. No. 3,239,420).
With increased use of soft gelatine capsules efforts have been made to obtain more chemically resistant capsule walls in order to obtain a stability satisfying the demands raised by extreme conditions, such as in tropical climates, or in the case of particularly sensitive active ingredients.
This problem was attempted to be solved by using a negatively charged organic hydrophilic polymer (see U.S. Pat. No. 2,800,457) or a negatively charged inorganic hydrophilic polymer (see U.S. Pat. No. 3,697,437) instead of phase-separating agents such as inorganic salts that were used earlier in encapsulating processes.
The additives mentioned above form a complex with the positively charged hydrophilic polymer (gelatine) of the capsule wall; thus, the inner wall of the capsule formed by this complex renders the entire wall more resistant to environmental influences.
There are also processes providing the capsule with a suitable outer coat. According to British patent No. 1,159,236, a coat of methacrylic acid or methyl methacrylate is used for this purpose. A coat prepared form silicone resin was also described for the same purpose (Pharm. Ind. 1954, 518-520).
A drawback of the above processes that are aimed at increasing the stability of soft gelatine capsules is that, in addition to the gelatine, the use of another materials is also required.